Lighting apparatuses with light emitting diodes (LEDs) have been gaining attention as a new light source because of excellent properties in terms of light emitting efficiency and longevity in comparison with incandescent lamps or halogen lamps. In order to improve light output of this kind of lighting apparatus, a quick solution is to mount LEDs in high density. However, this solution is not very realistic due to current issues regarding production cost and heat dissipation in driving when LEDs are mounted in high density. A more realistic solution in order to enhance the light output is to make luminous efficiency of an LED as high as possible. Various attempts have been made to this end, and two key parameters in making such attempts are Internal Quantum Efficiency (IQE) and External Quantum Efficiency (EQE).
The IQE is a parameter indicating the amount of light generated in a luminous layer of an LED to the amount of electric power that is supplied to the LED. The IQE is affected by the crystallinity of a semiconductor and the structure of the luminous layer that constitute the LED.
On the other hand, the EQE is a parameter indicating an amount of light emitted outside the LED to the amount of supplied electric power, and expressed by a product of the IQE and light extraction efficiency (a proportion of the amount of light emitted outside the LED in the amount of light generated in the LED). The light extraction efficiency is affected by the shape of a bare chip, the material that covers the bare chip, and the shape of the material. In order to improve the light extraction efficiency, it is common to cover a bare chip with resin so as to minimize the refractive index difference at a boundary between the bare chip and outside of the bare chip as much as possible.
Moreover, in a case of lighting apparatuses using LEDs, it is common for a light extracting surface of a bare chip to have depressions so that an incident angle of light on the light extracting surface is not fixed to one angle, thus improving the light extraction efficiency (Japanese Patent No. 2836687, and Compound Semiconductor, Vol. 8, No. 1, pp. 39-42, 2002).
As a method of mounting a bare chip on amounting substrate, flip-chip bonding as shown in FIG. 20 is commonly employed. In the flip-chip bonding as illustrated in FIG. 20, a vacuum collet 1300 sticks to a light extracting surface of a bare chip 1100, and the bare chip 1100 is joined with a wiring layer 1210 of a mounting substrate 1200 using ultrasonic bonding. By mounting the bare chip 1100 in this way, the distance between a light emitting layer of the bare chip 1100 and the mounting substrate 1200 is shortened, thus making it possible to effectively dissipate the heat generated in the light emitting layer. In other words, the flip-chip bonding is very effective for a lighting apparatus that requires LEDs in high density, in order to ensure a high heat dissipation capacity.
However, mounting bare chips having depressions on the light extracting surface using the flip-chip bonding often causes problems such as decreases in positioning accuracy and bonding strength, and destruction of the depressions. Specifically, as shown in an enlarged view in the circle in FIG. 20, depressions 1111 make it difficult for the vacuum collet 1300 to stick to the bare chip 1100 without fail, and for ultrasonic waves to propagate from the vacuum collet 1300 to the bare chips 1100 sufficiently for bonding. The same kind of problems also occur in display apparatuses having bare chips.